Metabolic Adaptation to Climate and Distribution of the Raccoon Procyon Lotor and Other Procyonidae

Part 1

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SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY · NUMBER 542

Metabolic Adaptation to Climate and Distribution of the Raccoon Procyon lotor and Other Procyonidae

John N. Mugaas, John Seidensticker, and Kathleen P. Mahlke-Johnson

SMITHSONIAN INSTITUTION PRESS Washington, D.C. 1993

ABSTRACT

Mugaas, J. N., J. Seidensticker, and K. Mahlke-Johnson. Metabolic Adaptation to Climate and Distribution of the Raccoon Procyon lotor and Other Procyonidae. Smithsonian Contributions to Zoology, number 542, 34 pages, 8 figures, 12 tables, 1993.--Although the family Procyonidae is largely a Neotropical group, the North American raccoon, Procyon lotor, is more versatile in its use of climate, and it is found in nearly every habitat from Panama to 60°N in Canada. We hypothesized that most contemporary procyonids have remained in tropic and subtropic climates because they have retained the metabolic characteristics of their warm-adapted ancestors, whereas Procyon lotor evolved a different set of adaptations that have enabled it to generalize its use of habitats and climates. To test this hypothesis we compared Procyon lotor with several other procyonids (Bassariscus astutus, Nasua nasua, Nasua narica, Procyon cancrivorus, and Potos flavus) with respect to (1) basal metabolic rate ([.H]{b}), (2) minimum wet thermal conductance (C{mw}), (3) diversity of diet (D{d}), (4) intrinsic rate of natural increase (r{max}), and, where possible, (5) capacity for evaporative cooling (E{c}). We measured basal and thermoregulatory metabolism, evaporative water loss, and body temperature of both sexes of Procyon lotor_ from north central Virginia, in summer and winter. Metabolic data for other procyonids were from literature, as were dietary and reproductive data for all species.

Procyon lotor differed from other procyonids in all five variables. (1) Procyon lotor's mass specific [.H]{b} (0.46 mL O{2}·g^{-1}·h^{-1}) was 1.45 to 1.86 times greater than values for other procyonids. (2) Because of its annual molt, Procyon lotor's C{mw} was about 49% higher in summer than winter, 0.0256 and 0.0172 mL O{2}·g^{-1}·h^{-1}·°C^{-1}, respectively. The ratio of measured to predicted C{mw} for Procyon lotor in winter (1.15) was similar to values calculated for Potos flavus (1.02) and Procyon cancrivorus (1.25). Values for other procyonids were higher than this, but less than the value for Procyon lotor (1.76) in summer. On a mass specific basis, Bassariscus astutus had the lowest C{mw} with a ratio of 0.85. (3) Procyon lotor utilized three times as many food categories as Procyon cancrivorus, Nasua nasua, and Bassariscus astutus; about two times as many as Nasua narica; and nine times as many as Potos flavus. (4) Intrinsic rate of natural increase correlated positively with [.H]{b}. Procyon lotor had the highest r{max} (2.52 of expected) and Potos flavus the lowest (0.48 of expected). The other procyonids examined also had low [.H]{b}, but their r{max}'s were higher than predicted (1.11-1.32 of expected). Early age of first female reproduction, fairly large litter size, long life span, high-quality diet, and, in one case, female social organization all compensated for low [.H]{b} and elevated r{max}. (5) Although data on the capacity for evaporative cooling were incomplete, this variable appeared to be best developed in Procyon lotor and Bassariscus astutus, the two species that have been most successful at including temperate climates in their distributions.

These five variables are functionally interrelated, and have co-evolved in each species to form a unique adaptive unit that regulates body temperature and energy balance throughout each annual cycle. The first four variables were converted into normalized dimensionless numbers, which were used to derive a composite score that represented each species' adaptive unit. Procyon lotor had the highest composite score (1.47) and Potos flavus the lowest (0.39). Scores for the other procyonids were intermediate to these extremes (0.64-0.79). There was a positive correlation between the number of climates a species occupies and the magnitude of its composite score. Linear regression of this relationship indicated that 89% of the variance in climatic distribution was attributed to the composite scores. Differences in metabolic adaptation, therefore, have played a role in delimiting climatic distribution of these species.

It was clear that Procyon lotor differed from the other procyonids with respect to thermoregulatory ability, diet, and reproductive potential. These differences have enabled it to become a highly successful climate generalist, and its evolution of an [.H]_{b} that is higher than the procyonid norm appears to be the cornerstone of its success.

OFFICIAL PUBLICATION DATE is handstamped in a limited number of initial copies and is recorded in the Institution's annual report, Smithsonian Year. SERIES COVER DESIGN: The coral Montastrea cavernosa (Linnaeus).

Library of Congress Cataloging-in-Publication Data

Mugaas, John N.

Metabolic adaptation to climate and distribution of the raccoon Procyon lotor and other Procyonidae / John N. Mugaas, John Seidensticker, and Kathleen P. Mahlke-Johnson.

p. cm.--(Smithsonian contributions to zoology; no. 542)

Includes bibliographical references (p. )

1. Raccoons-Metabolism-Climatic factors. 2. Procyonidae-Metabolism-Climatic factors. 3. Raccoons-Geographical distribution. 4. Procyonidae-Geographical distribution. I. Seidensticker, John. II. Mahlke-Johnson, Kathleen. III. Title. IV. Series.

QL1.S54 no. 542 [QL737.C26] 591 s-dc20 [599.74´443´04542] 93-3119

Contents

Page Introduction 1 Defining the Problem 1 Procyonid Origins 1 Typical Procyonids 2 The Atypical Procyonid 3 The Hypothesis 4 Hypothesis Testing 4 Adaptive Significance of the Variables 4 Basal Metabolic Rate and Intrinsic Rate of Natural Increase 4 Minimum Thermal Conductance 4 Capacity for Evaporative Cooling 5 Diet 5 Experimental Design and Summary 5 Acknowledgments 5

Materials and Methods 6 Live-trapping 6 Metabolic Studies 6 Basal and Thermoregulatory Metabolism 6 Evaporative Water Loss 7 Body Temperature 7 Calibrations 7 Calorimeter 7 Body Temperature Transmitters 8 Statistical Methods 8 Estimating Intrinsic Rate of Natural Increase 8 Comparison of Adaptive Units 8

Results 8 Body Mass 8 Basal Metabolic Rate 9 Minimum Thermal Conductance 9 Evaporative Water Loss 11 Thermoregulation at Low Temperatures 12 Body Temperature 12 Summer 14 Winter 14 Thermoregulation at High Temperatures 16 Body Temperature 16 Summer 16 Winter 16 Daily Cycle of Body Temperature 16

Discussion 16 Basal Metabolic Rate 16 Background 16 Captive versus Wild Raccoons 17 Seasonal Metabolism of Raccoons 17 Comparison of Procyon lotor with Other Procyonids 17 Influence of Diet on Basal Metabolism 18 Background 18 Food Habits of Procyonids 18 Food Habits and Basal Metabolism 19 Summary 19 Basal Metabolism and Intrinsic Rate of Natural Increase 19 Background 19 Procyon lotor 19 Bassariscus astutus 19 Nasua narica 19 Nasua nasua 20 Procyon cancrivorus 20 Potos flavus 20 Summary 20 Basal Metabolism and Climatic Distribution 21 Procyon lotor 21 Other Procyonids 21 Minimum Thermal Conductance 21 Background 21 Effect of Molt on Thermal Conductance 21 Comparison of Thermal Conductances 22 Procyon lotor versus Tropical Procyonids 22 Bassariscus astutus 22 Thermoregulation and Use of Stored Fat at Low Temperatures 22 Background 22 Thermoregulation 22 Stored Fat 23 Thermal Model of the Raccoon and Its Den 23 Metabolic Advantage of the Den 23 Thermoregulation at High Temperatures 24 Background 24 Comparison of Procyonid Responses to Heat Stress 24 Potos flavus 24 Nasua nasua and Nasua narica 24 Bassariscus astutus 24 Procyon lotor 24 Procyon cancrivorus 24 Summary 24 Composite Scores of Adaptive Units and Geographic Distribution 25 Evolution of Metabolic Adaptations 26 Evolution of Low Basal Metabolic Rate 26 Evolution of High Basal Metabolic Rate 27 Summary 28

Appendix: List of Symbols 29

Literature Cited 30

Metabolic Adaptation to Climate and Distribution of the Raccoon Procyon lotor and Other Procyonidae

John N. Mugaas, John Seidensticker, and Kathleen P. Mahlke-Johnson

John N. Mugaas, Department of Physiology, Division of Functional Biology, West Virginia School of Osteopathic Medicine, Lewisburg, West Virginia 24901. John Seidensticker and Kathleen P. Mahlke-Johnson, National Zoological Park, Smithsonian Institution, Washington, D.C. 20008.

Part 2

$Introduction$

DEFINING THE PROBLEM

Procyonid Origins

The major carnivore radiations took place about 40 million years before present (MYBP) in the late Eocene and early Oligocene (Ewer, 1973:363; Wayne et al., 1989). Between 30 and 40 MYBP, a progenitor split into the ursid and procyonid lineages, which evolved into present-day bears, pandas, and raccoons (Wayne et al., 1989). The taxonomic relatedness of pandas to bears and raccoons has been tested extensively and a number of authors have summarized current thinking on the problem (Martin, 1989; Wayne et al., 1989; Wozencraft, 1989a, 1989b; Decker and Wozencraft, 1991). Davis (1964:322-327) and others (Leone and Wiens, 1956; Todd and Pressman, 1968; Sarich, 1976; O'Brien et al., 1985) place the giant panda, Ailuropoda melanoleuca, with the ursids. The taxonomic status of the red panda, Ailurus fulgens, appears to be less certain. Some current investigations align the red panda with bears (Segall, 1943; Todd and Pressman, 1968; Hunt, 1974; Ginsburg, 1982; Wozencraft, 1984:56-110; 1989a), whereas others place them intermediate to procyonids and bears (Wurster and Benirschke, 1968; Sarich, 1976; O'Brien et al., 1985), or in close relationship to the giant panda (Tagle et al., 1986).

The procyonid radiation took place in North America and produced forms that were mostly arboreal and omnivorous (Eisenberg, 1981:122; Martin, 1989). The center of this diversification occurred in Middle America (Baskin, 1982; Webb, 1985b) during the Miocene (Darlington, 1963:367; Webb, 1985b). Fossil procyonids from the late Miocene are represented in Florida, California, Texas, Nebraska, Kansas, and South Dakota (Baskin, 1982; Martin, 1989) and include such genera as Bassariscus, Arctonasua, Cyonasua, Paranasua, Nasua, and Procyon (Baskin, 1982; Webb, 1985b). During the Miocene procyonids underwent a modest radiation within tropical and subtropical climates of North America's central and middle latitudes. Cyonasua, which has close affinities to Arctonasua (Baskin, 1982), appears in tropical South America in the late Miocene and immigrated there either by rafting across the Bolivar Trough or by island-hopping through the Antilles archipelagoes (Marshall et al., 1982; Marshall, 1988). Thus, procyonids were found on both continents prior to formation of the Panamanian land bridge (Darlington, 1963:367, 395; Marshall et al., 1982; Marshall, 1988). Origins of Bassaricyon and Potos are obscure but probably occurred in tropical rainforests of Middle America (Baskin, 1982; Webb, 1985b). A subsequent Pleistocene dispersal carried several modern genera (Table 1) across the Panamanian land bridge into South America (Webb, 1985b). Bassariscus and Bassaricyon represent the most primitive genera in Procyoninae and Potosinae subfamilies, respectively (Table 1; Wozencraft, 1989a; Decker and Wozencraft, 1991).

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